LED chips are increasingly being used for illumination and lighting purposes. For example to create white light, blue or UV LEDs coated with phosphor are used, so-called phosphor converted LEDs. The phosphor converts at least some of the blue radiation to for example yellow light. Together, the non-converted blue light and the yellow light generate a white light.
However, individual LED chips do currently not provide sufficient brightness for many applications, like projections displays and car head lighting. Therefore, LED devices comprising arrays of LED chips are used, for example as disclosed in the document U.S. Pat. No. 6,325,524. In U.S. Pat. No. 6,325,524, as well as in many other known multi LED chip devices, several LED chips are positioned besides each other on a substrate. The light from the LED chips is then collected by an optical system covering the LED chips. However, due to the wide extension of the optical system covering all the LED chips, there is a low amount of light per unit of surface area, resulting in low brightness.